Ch 11 – Gene Expression

The control of a gene at transcription, translation for even the polypeptide.

Prokaryotes (Bacteria)

Operons – control of transcription

• These comprise of a structural gene, operator and promoter.

• Promoter region organizes RNA polymerase and starts transcription.

• Operator region is binding site for a repressor protein. This protein will stop RNA polymerase from binding.

• Also involved is a regulator gene that codes for that repressor protein.

• These proteins have binding sites for a particular molecule.

• The binding of that molecule will make the repressor protein release from the operator.

• Example from the book (lac operon)

• Repressor protein is attached to operator.

• Lactose will bind to the repressor protein causing it to release from the operator and transcription begins.

• The protein formed is a lactose metabolizing protein.

• It is important to control the production of protein until they are needed. Why?

Energy (ATP)

Eukaryotes use different systems

1. Control of transcription

• In eukaryotic cells, RNA polymerase need transcription factors to attach RNA polymerase to the promoter region on the DNA.

• These factors can “hold” RNA polymerase ready to transcribe a gene.

• “Up stream” of the promoter and structural gene is the enhancer region. Other transcription factors bind here and act as activators.

• When the DNA is bent by bending proteins the transcription factors are brought together and the RNA polymerase is allowed to transcribe the structural gene.

2. Control after translation

• The mRNA (pre-mRNA) is made up of exons and introns.

• Exon (EXpressed) are translated into proteins.

• Introns (INtervening) are removed and not translated.

The introns are removed, the exons assembled together and the new mRNA is translated.

3. Epigenetics

• The control of genes form outside “on top” of the genome.

• Environmental conditions can change the function of your DNA by changing your epigenome (and your offspring).

• Methyl groups can be added to cytosines and adenines turning off the gene. (This could be good or bad)

• Tight coiling of areas of DNA prohibit the promoter region being accessed and thus stopping transcription of the gene. Histones

4. Homeotic Genes

• Regulatory genes that control the pattern of body formation during early development.

• legs, wings, body segments, etc.

5. Protein Modification

• Modification of proteins

• Insulin